1. Field of the Invention
The present invention relates generally to pressure gauges and more particularly to a low pressure safety indicator, which is incorporated into a tire valve cap for a tire valve stem.
2. Description of the Prior Art
As highways become ever more crowded, safety becomes ever more important for the millions of people who use automobiles for transportation. Improper tire pressure is a major cause of tire malfunction and can also have a significant effect on gas mileage achieved by the vehicle. A tire that is under-inflated causes more drag, more friction and more heat, thus rolls less efficiently than a tire with proper inflation. In extreme cases, under-inflation can result in wear and over heat on improper portions of the tire and can even contribute to blow-outs. Thus, it is very important that drivers have an easy and convenient way to monitor the low pressure in their vehicle's tires.
The conventional device for checking tire pressure is the well-known “tire pressure gauge”, which is applied to the valve stem of each tire in turn. Internal pressure forces a tire pressure gauge indicator to emerge from the gauge's casing, and the tire pressure gauge indicator includes markings or digital numbers which indicate the level of pressure in the tire. However, each valve stem generally includes a valve cap, which keeps grit and road grime from getting into the tire valve. In order to measure the tire pressure, this valve cap must be removed, and placed in a safe place, while the tire pressure gauge is pressed onto the valve stem. There is usually some loss of pressure during this operation, which can be unfortunate for some tires which have borderline low pressure to begin with. Additionally, the application of the gauge generally requires the user to kneel or stoop on the roadway near the tire, which can be awkward and messy, and damaging to clothing. At a minimum, the user's hands generally become soiled to some degree, and the markings on the stick tire gauge can be difficult to make out, especially in dim light. Consequently, many users find it inconvenient to make proper pressure checks and the tire pressure of many vehicles are under-inflated. Recent legislation in the U.S. (namely the Transportation Recall Enhancement, Accountability, and Documentation, or “TREAD” act), has mandated the use of tire valve caps with low pressure warning indicators to correct this problem.
Thus, there is a need for a tire valve cap which does not require removal from a valve stem, is easy to use to check tire pressure and does not require the user to get messy in order to properly inflate a tire. The user is thus encouraged to monitor pressure more closely and may travel more safely.
There have previous attempts to develop more convenient tire pressure indicators which address some of these concerns. In particular, U.S. Pat. No. 1,494,001 to McPherson discloses a combined dust cap and tire gauge having numerical values which are displayed by markings on the exterior of the cap in response to internal tire pressure. This has the disadvantage of being difficult to read from a distance or in dim light. U.S. Pat. No. 5,083,457 to Schultz discloses a remotely actuated tire pressure sensor having a transducer mounted on a tire stem which sends information to a hand-held remote display unit. This includes electronics which may be fragile and costly to manufacture, and requires the use of a remote display unit, which may become lost or damaged. U.S. Pat. No. 6,525,655 to Huang discloses a diaphragm-type tire pressure gauge which can include an internal rod which is advanced by air pressure from a tire to display various colors or marked with data units. An alternate of Huang includes an LED which is activated by tire pressure. This however, requires electronics including a power supply of some sort, and can be expected to be costly and relatively difficult to manufacture.
Thus, there is a need for a tire valve cap which uses a simple mechanical mechanism without external power which is easy and inexpensive to use, allows easy addition of air to the tire, presents an easily readable low pressure safety indication and is less susceptible to become unreadable or discolored than prior devices.